Conventional syringes provide frequent risk when manipulated in their intended use, also unfortunately sometimes during unintended reuse and always during disposal. In using a conventional syringe, the syringe is packaged empty and must be filled by fluid communication with an ampoule. The ampoule is configured as a container sealed by a rubber dam which is to be perforated by a needle attached to the syringe.
The contents within the ampoule is in an air-tight container. Consequently, one extracting a dose of fluid from the ampoule will generate a negative pressure if the syringe is first inserted into the ampoule while the piston of the syringe is in a fully "closed" position, i.e. no air space exists between the piston and the needle carried on the cylinder. As a result, many people who use syringes to extract fluids from ampoules will begin with the piston of the syringe in an intermediate position and push air into the ampoule creating a positive pressure. This makes it easier to withdraw fluid from the ampoule.
It is to be noted, however, that the air that is thus injected into the ampoule is a contaminant, since normal air in an every day environment is filled with particulate contaminants which necessarily become transmitted into the ampoule. In a medical care environment, such as in a hospital or doctor's office, it may even be more likely that the contaminant could foster pathogens. Thus, subsequent users of the ampoule are faced with the real possibility that a contaminant injected into the ampoule during a prior excursion into the ampoule will be passed onto a subsequent user of the medication.
Since the conventional syringe utilizes a piston which reciprocates within a cylinder, the conventional syringe adapts itself to reuse multiple times. There is no impediment inherent in the construction of a syringe which precludes its subsequent use by others. It is common knowledge and has been widely reported that reuse by third parties provides unwanted risks in spreading disease.
Another problem associated with an ampoule-type of system involves the requirement that the dose administrator exercise extreme care in aligning the needle at all times, such as with respect to the rubber dam of the ampoule. Inadvertent needle sticks can have dire consequences.
In all cases, in order to effectively utilize the syringe, the needle must first have been placed on the syringe body. This is typically performed by a luer coupling which unites a base of the needle to a tip of the syringe. Once the syringe has been equipped with the needle, extraordinary care must be exercised to prevent unwanted needle sticks such as described earlier. Frequently, the syringe is loaded with medicating fluid at a site remote from the patient who is to receive the dose. When this is the case, a syringe equipped with a needle must be transported to the patient. Most systems provide for a needle cap to be placed back over the needle to guard against unintended contact. Problems with inadvertent needle sticks when replacing a needle cap are quite common.
Even after "uneventful" utilization of the syringe on the patient, the problems associated with disposal of the needle and syringe are more complex since this system has now been further compromised by contact with the patient. Extraordinary attempts in adequately disposing of hazardous medical waste, including used syringe and needle systems are well documented in both the patent literature, the media, the medical literature and elsewhere.
It appears that a solution to the longstanding problem of disposing of medical wastes continues to evade resolution both as to individual use and as to hazardous waste treatment despite strong incentives now in place in the medical community to minimize the need for and utilization of needles whenever possible. One result has been a trend to embrace needleless systems whenever possible or to tailor systems which call for infrequent needle use.
One common scenario that lends itself to a substantially "needleless" systems involves patients in medical facilities such as hospitals who receive periodic doses of liquids intravenously. It is quite common to install a catheter in a patient intravenously and then access the catheter for subsequent doses of liquid rather than search for another site for each subsequent injection. Unfortunately, many systems using catheters still require the use of a syringe equipped with a needle in order to access the catheter itself.
Another problem with accessing a catheter is that it is used intermittently. There is a natural tendency of the patient's system to view the installed catheter as the foreign body that it is. Therefore, the site where the catheter communicates with the blood in a vein is susceptible to clotting. Administering liquid when the outlet end of the catheter has partially clotted closed increases the likelihood that a blood clot would be dislodged from the catheter and sent coursing through the venous system of the body. Consequently, extreme care is required when administering a dose through a syringe via a catheter in order to sense the presence of a restriction which suggests a clot at the outlet end of the catheter. Experienced personnel should perceive increased back-pressure or resistance when advancing the plunger of the piston within the cylinder. Sensing back-pressure is somewhat intuitive and certainly benefits from experience.
A certain degree of tactile feedback can be perceivable when using a conventional syringe. Since the cross-section of the liquid changes as it moves from the cylindrical portion of the syringe through its tapering conical section at the outlet, the liquid's velocity increases as it is forced out of the syringe. Should an uncharacteristic resistance be perceived during an injection into a catheter, care must be taken that a blood clot is not being dislodged. Blood thinning agents would then have to be administered or, alternatively, if the clot is still perceived connected to the catheter, the catheter should be removed in favor of a new catheter. When a "long line" catheter system is used, appreciable time and resources of the hospital staff will have been required to reinstall the long line, which sometimes spans from a patient's leg into the patient's heart.
The following prior art reflects the state of the art of which applicant is aware and is included to discharge applicant's acknowledged duty to disclose relevant prior art. It is respectfully submitted, however, that none of the patents teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as set forth in detail hereinafter and claimed with specificity.
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